whoever replied to you literally explained the same thing I did to you?Participation<-参加/参戦<-taiban
As I stated before “to perform with”
Not the actual event, that is already implied, taiban does not mean the event itself😅
You know our bassists is from early 90s era, I hangout with 80s rockers,punks/pschobilly, make music for idols, and have been speaking Japanese everyday for about 8 years so 
I know there is a big difference from translation to actually thinking in a language so once again reread your friend’s words 
"イベントに参加”や“イベントに参戦”って
Key part to understand “ibento ni<-”
Is not him saying it means event.
Participation<-参加/参戦<-taiban.
In translation mode you are searching to only support what thought was right maybe?
対バン=performing with a band, regardless of genre, or whatever kind of event it is, it is not a specific event or means event like you said, can be used when talking about >performing with< at any event with at least one other band/performer.
イベント: usually four or more bands.
Any less goes into 3 man, 2 man.
和製英語と思えばいい、think of イベント as english gaining a specific Japanese meaning added on.
You also said:
Taiban also stands for a Japan only venue system;
However it’s a weird outdated and complex system. (which is a reason why bands disband but also why live venues disappear.
<<<>>>
Thats not right either:sweat_smile:
Lets not get into livejournal/geocities era misinformation as fact for vk/jrock.
Noruma and booking system has nothing to do with the usage of the word Taiban.
Example: we were invited by AREA to play for free last month, no noruma, out of respect. To one artists there I said:
“あぁ久しぶりに対バン出来た嬉しい!”
“Aa hisashiburi ni taiban dekita ureshii”
“Ah, im happy we can “perform together” again after a long time!”
The noruma, booking system, of it was event, 3man, 2man has no weight on the word-> performing together,participating together.
Stating noruma is why businesses is failing is a doozie too but for the OP
and anyone else trust me haha, 白人だから言う事聞けんかもだけど一応先輩だぞ?! 
日本でプロ活動やると"対バンの意味"って、あたり前田のクラッカーだよ👯♀
I may be a white boy over here but if you do pro activities here knowing the nuance of a simple word like taiban is a piece of cake:pray: all said with love! 